The TOBI is a well known device, which may be known by different names, that is utilized to provide cooling air to the turbine of the gas turbine engine. An example of the TOBI is shown in U.S. Pat. No. 4,526,511 granted to R. Levine on July 2, 1985 and assigned to United Technologies Corporation, the assignee common to this patent application, which should be referred to for more details. In particular, the inlet of the TOBI receives air from the compressor or a source of cooling air and passes it through annular spaced nozzles that impart a swirling moment and directs the discharging stream tangentially to the rotating turbine. The velocity, amount and direction of the cooling air is very important as viewed from the effectiveness of its cooling capacity and its effect to the overall engine performance. It is extremely important that only the correct amount of air be utilized as any additional air would be a penalty to the performance of the engine or too little air would result in overheating of the turbine or requiring the temperature of the gas stream to be reduced again impacting engine performance. Hence, ideally the TOBI will optimize the use of turbine cooling air in order to minimize the cooling air temperature.
Essentially, the air discharging from the TOBI is delivered into a cavity just ahead of the turbine. The cavity is typically sealed off by seals (generally labyrinth type) that interface between the rotating and non-rotating structure. Inasmuch as seals have some leakage, the air discharging through the TOBI in heretofore known designs escape from the cavity through the seals resulting in an adverse effect on the performance of the TOBI.
The arrows in FIG. 1 demonstrate the effect the seals have on the plume of the cooling air discharging from the TOBI. As noted, the turbine 10 (partially shown) comprises the disk 14 supporting a plurality of circumferentially spaced blades 16 (one being shown). The inner seal 18 and outer seal 20 define an annular cavity 22 just ahead of the turbine. The TOBI 24 which comprises an annular passageway 26 receives the compressor discharge air and delivers it to the turbine rotor through a plurality of nozzles 28.
The arrows illustrating the plume of the air discharging from the TOBI illustrate graphically the effect the leakage has on the plume and, as noted, is significantly wide.
We have found that we can reduce the plume size and consequently reduce the temperature of the cooling air supplied to the turbine (by virtue of reducing the air pumping effect from the disk) by providing apertures in the TOBI upstream of the nozzles and judiciously sizing and orienting these apertures so as to create tangential jet streams of air that pressurize the cavity in proximity to the seal.